My gut feeling (and it's nothing more than that) is that Chevy has already dangled that carrot in front of him, possibly more than once. I suspect that Kane simply DGAF at this point, and wants to do whatever he can to force a trade.
IF that's the case (and I really have no idea one way or the other), then they need to trade him ASAP even if it's an underpayment. An underpayment would really suck, but if a guy has an attitude like that he'll do more damage than good no matter how skilled he is.
I'm not saying I think this. From what I've seen of Kane in interviews and such off the ice he seems like a decent guy but of course such interviews are kind of meaningless. Just saying that if Chevy does pull the trigger on a deal that appears less than fair market value, this might explain it although TNSE is too classy of an organization to openly say that's why they did such a trade.
As someone who also follow the Leafs casually, I can say that skilled players with bad attitudes can definitely do more harm than help. I think Chevy has managed the team with a steady hand so I'm prepared to trust him to do the right thing here.